Siloxane/graphene oxide (GO) nanocomposites were synthesized by hydrolysis and condensation of tetraethyl orthosilicate in the presence of GO nanosheets through a sol-gel process. The influence of synthesis parameters on the properties of the siloxane/GO samples was studied and their structural, morphological and physicochemical characteristics were compared using various techniques. Polyether sulfone-supported GO and siloxane/GO thin film membranes were prepared using a pressure-assisted self-assembly method using a dead-end cell, and their separation performance and antifouling ability were evaluated. Siloxane/GOs appeared to have higher interlayer spacing, higher zeta potential and thus higher dispersion stability in aqueous media compared to GO. This gave rise to slower and more uniform sedimentation of the siloxane/GOs during the filtration process and formation of thin film membranes possessing denser and smoother morphology. The porosity, mean pore radius, water contact angle and pure water flux of the prepared membranes were compared. The separation performance of the prepared membranes to remove methylene blue (MB) and penicillin G-procaine (PG-P) from water was evaluated as a function of used GO solution concentration. The antifouling ability of membranes was studied by determining reversible fouling (Rr), irreversible fouling (Rir) resistances and flux recovery ratio (FRR). The siloxane/GO thin film membranes containing larger siloxane network exhibited the highest rejection percentage for MB (~99%) and PG-P (~88%), which were about 40% and 90% higher than that achieved for GO thin film membranes, while the water flux remained as high as 78.1 l·m-2h-1. Furthermore, these membranes exhibited the highest chlorine resistance, stability under ultrasonication, FRR (89%) and Rr (57%) values, implying higher chemical and mechanical stability, flux recovery capacity and antifouling ability.